The Origin and Evolution of Titan

International audienceSaturn's moon Titan is the second largest natural satellite in the solar system, and the only one that possesses a substantial atmosphere. The origin of the massive nitrogen atmosphere and the source of the present-day methane, which is continuously destroyed by UV-driven photochemistry, has long been debated. Data collected by the Cassini-Huygens mission since its arrival to Saturn in 2004 now provide key constraints on Titan's atmosphere composition, surface morphology and interior structure, which restrict the possible scenarios of formation and evolution. In the present chapter , after reviewing our present knowledge about the interior structure and composition based on the Cassini-Huygens data, we present the different physical and chemical processes that have potentially affected the origin and evolution of Titan. In particular, we argue that all along Titan's evolution , from accretion to present, interactions between the icy shell, the internal water ocean and the deep rock-dominated interior may have affected the evolution of the atmosphere. In spite of considerable progresses in our understanding of Titan thanks to Cassini-Huygens, many questions still remain , and we conclude on how they may be addressed by future exploration missions